Process for disintegrating dry cellulose pulp

ABSTRACT

A process is provided for producing disintegrated (fluffed) dry cellulose fibers from baled cut pulp sheets for use in products such as diapers, absorbent pads and rolls, and the like. The sheets are shredded into particles and subsequently fed in a carrier gas stream to a disc mill with a gap width within the range of 0.1 to about 0.5 mm. wherein the shredded particles are milled until disintegrated and the fibers liberated. The fibers are then removed by the gas stream.

Inventors Appl. No.

Filed I Patented Assignee Priority Nils Verner Blomqvist Ornskoldsvik;

lngemar Liss-Albin Croon, Aliredshem; Lars Goran Eriksson. Vasterhus. all of, Sweden Aug. 14, 1967 Aug. 3, 1971 Mo Och Domsjo Aktiebolag Ornskoldsvik, Sweden Aug. 17, 1966 Sweden PROCESS FOR DISINTEGRATING DRY [50) FieldofSearch 241/3,28, 29, 152, 152 A [56] References Cited UNITED STATES PATENTS 1,880,045 9/1932 Richter 241/(28 UX) 2,035,994 3/1936 Sutherland. 241/260 X 2,364,721 12/1944 Kassay 241/28 X 2,444,929 7/1948 Hatch 241/28 X 2,513,344 7/1950 McEwen 241/(3 UX) Primary Examiner-Donald G. Kelly Attorney-lanes & Chapman ABSTRACT: A process is provided for producing dis integrated (fluffed) dry cellulose fibers from baled cut pulp sheets for use in products such as diapers, absorbent pads and g v frolls, and the like. The sheets are shredded into particles and l chlmss Draw: subsequently fed in a carrier gas stream to a disc mill with a U.S. C1. 241/28, g p id i in h r ng f .1 to about mm"- h in 241/29, 241/152 the shredded particles are milled until disintegrated and the Int.Cl. B02c 7/06, fi r li Th fibers r h n r m by he gas B02c 13/288, B02c 21/00 stream.

. Sheet 1 Pulpbole feeder Disk refiner Disv qteriql FOCESSI refiner p Disk i refiner PATENTED AUG 3|97l 3,596,840

SHEET 1 UF 3 Fig.1

Sheet Pulpbflle feeder Disk Shredder refiner oteriol Co l l g Dlty processi in refiner 3 6 Disk e refiner 2/ PATENTEB AUG 3191a SHEET 3 OF 3 Fig. 5

PROCESS FOR DISINTEGRA'I'ING DRY CELLULOSE PULP It is understood that disintegrating cellulose pulp to fluff means that the-pulp is broken up so that the fibers are laid bare while simultaneously trying to avoid fiber cutting and formation of fiber bundles. I

1n previously known processes for producing disintegrated dry cellulose pulp, rolls are used as starting material. But thereby the original pulp roll with the same width as the drying machine must primarily be divided into smaller pulp rolls which have a width of 14-15 cm. and a diameter of about 100 cm. The pulp has, as a rule, a weight of 700-800 g./m. 1n disintegrating the roll pulp it is fed'to a disintegrator which may be a hammer mill, a pin mill or a disk refiner and the resulting fluff is fed by means of carrier air to the equipment for manufacturing those products in which the cellulose fluff shall be included.

By using said conventional method it is necessary to use loosely compressed roll pulp, otherwise very large amounts of fiber bundles are obtained in the resulting fluff. By producing roll pulp for the above-mentioned purpose it is therefore necessary to keep the compressive pressure in the press section of the wet press machine low to avoid the formation of fiber bundles. Accordingly the pulp leaving the press section will contain large amounts of water which must be removedand therefore the drying time is prolonged and larger amounts of steam than nonnally are required in the drier section of the wet press machine to dry the pulp. Thus, the restriction to the use of roll pulp means a great disadvantage economically as the lower compressive pressure gives rise to a considerably higher price on roll pulp than on sheet pulp of corresponding quality. The finished rolls are further more voluminous than pulp in baleform and take up larger room at transports and storing. All these factors give rise to that the price of roll pulp is about $40 higher per metric ton than of sheet pulp of a corresponding quality. Another disadvantage of the known method is that it, despite the use of special pulp, is impossible to avoid the fonnation of large amounts of fiber bundles in the resulting fluff which can contain up to 30-40 percent of such bundles. These fiber bundles give rise to a slight formation of cracks in the finished products what in its turn causes a lower liquid absorption for these products.

It has now surprisingly been found that cellulose fluff can be advantageously produced starting from pulp in sheet form obtained by conventional methods if the pulp is shredded in dry v condition and then, still in dry condition, defibrated in a disk refiner. The use of a disk refiner as disintegrator in the production of fluff according to the present invention has proved to be very advantageous not only econoniically but also purely technically because disk refiners deliver a pulp containing only 10-15 percent' of fiber bundles which is much lower than in previously known methods in spite of the fact that a harder pressed pulp is used as starting material.

Despite the more effective defibration the risk for fiber cutting is not greater than in previously known methods. Further it is surprising that it is possible to treat dry pulpiin a'disk refiner in which otherwise only wet pulp can be treated. Earlier experiments have namely shown that the pulp is stopped in the refiner if the moisture content falls below a certain value and is burnt so that it sticks to the refiner. The processing of dry, shredded pulp according to the present invention involves cer tain requirements asto the milling disks of the refiner.

It is understood that disk refiner means an apparatus for disintegrating pulp comprising two opposite milling disks of which one is rotating and the other: commonly fixed. The opposite surfaces of the milling disks have milling means in the form of substantially radial and/or transverse bars, projections or similar. The pulp to be treatedis-fed through an opening at the center of the fixed milling disk into a central feeding chamber which is formed by opposite recesses in the central part. of the d'uks whereby the distance between the disks is greater in the central part and successively decreases outwards to turn into a rather narrow gap having parallel sides along the outer parts of the disks. Pulp is fed from the chamber outwards through the gap between the outer parts of I the two disks. A distributor, e.g. in the form of a spider, is usually mounted on the rotating disk in the feeding chamber to feed the pulp outwards. 1n the gapbetween the milling disks the pulp is subjected to the desired disintegration and is then fed peripherally in order to be removed through an opening in the housing surrounding the milling disks. The width of the gap is adjustable by axial displacement of one of the milling disks whereby the effect of the treatment can be controlled.

To be employed in the process according to the present invention the milling means ought to be substantially radial bars of substantially constant height over the fiat part of the disk;

which bars extend from the outer edge of the disk inwards and partly into the central recessin the disk, if desired in combination with lateral bars. lf transverse bars are used they ought to have a height decreasing from the periphery to the center of the disk so that they are level with the radial bars at the periphery but have lower height than these nearer the center. 1

The substantially radial bars should not run into each other near the center of the milling disk, the interspaces between them should instead be open inwards. Milling disks of the type which have short tooth shaped projections both in radial and peripheral direction and those having only peripheral bars have proved to be unsuitable for the invention as they are easily blocked and the pulp is burnt so that it sticks to the disks.

The width of the gap between the milling disks measured where the surfaces of the milling means are nearest each other is important for achieving a good result. The width of the gap should be from 0.1 to 5 mm., preferably 0.5-3 mm. The percentage of fiber bundles in the resulting fluff decreases with decreasing value of the width of the gap but the fiber cutting increases on the other hand wherefore a distance less than 0.1 mm. gives a disadvantageously high percentage of shortfibered pulp in the fluff and therewith lower bulk and somewhat poorer absorption characteristics. When the width of the gap exceeds 5 mm. the percentage of fiber bundles increases in an unacceptable degree.

The number of revolutions of the rotating milling disk should be 500-2000 r.p.m., preferably 1000-1800 r.p.m.

As being mentioned above the sheet pulp is subjected to shredding before being disintegrated in the disk refiner. This treatment may be carried out in any suitable shredder. A specially suitable type of shredder is the hammer-type mill or the pin-type mill. Such a shredder comprises a rotor with fixed or movable hammer-shaped milling means which operate against a fixed strainer. Shredders of this type have earlier been employed for the shredding of bark, pieces of wood, waste cardboard and waste paper and the like and have provided suitable for achieving a shredded pulp which can be fed to the refiner. The shredder should be provided with a strainer which does not let through too great pieces of pulp so that a suitable degree of shredding is achieved. The openings in the strainer should preferably be 1-5 cm., especially 2-3 cm.

To obtain the desired result the pulp must be dry at the arrival to the shredder and be maintained in dry condition during both the shredding and the disintegration in the refiner. Dry" is supposed to mean that the pulp has a dry content over percent by weight, preferably 88-96 percent by weight. Particularly suitable is a dry content of 93-95 percent by weight. These dry contents are normally obtained in the drier section by usual pulp manufacturing. If the dry content falls below 85 percent by weight the fibers are matted together and stop between the radial and transversal bars on the milling disks of the disk refiner whereby the pulp is burnt and sticks to the disks.

In a suitable apparatus for performing the process according to the invention as diagrammatically shown in FIG. 1 in the drawings a shredder I is provided to feed several disk refiners 2 via a collecting bin 3. The pulp bale 4 consisting of several sheets is brought in a sheet feeder 5 which successively feeds the sheets to the shredder 1. From there the shredded pulp is.

fed in the form of pieces. e.g. l-S cm. in dimension, to the collecting bin 3. The shredder and the collecting bin could be arranged so that the shredded pulp falls directly down into the bin from the shredder. The bin is provided with a number of outlets corresponding to the number of refiners 2. The pulp is fed from these outlets by means of suitable feeder rolls as screw-shaped rolls or taper pin rolls to conveyors which transfer the pulp to a feed screw which feeds the pulp into the center of the mill housing of the disk refiners. if desired, the refiners could be arranged directly below the collecting bin. From the refiners the fluff is fed by means of suitable transport devices to one or more processing machines 6 where it is processed to finished products. This last transport should preferably be carried out by means of carrier air by feeding the same to the screw conveyors for the shredded pulp or through an inlet in the housing of the refiner whereby the fluff is removed at the lower part of the housing.

A suitable shredder is shown in FIG. 2. It is provided with a rotor 7 having fixed or hinged hammers 8 which operate against a strainer through which the shredded pulp falls. As mentioned above the strainer should have openings from 1 to cm. and is preferably formed of curved rods mounted parallel to the main axis of the rotor and of transverse rods.

FIG. 3 shows diagrammatically a disk refiner comprising a housing 10, a fixed milling disk 11 and a rotatable milling disk 12. The pulp is fed through an inlet 13 and is distributed by means of a spider 14 mounted on the rotating milling disk. The resulting fluff is removed through the peripheral outlet 15.

A suitable embodiment of the milling disks is shown in FIG. 4. The shown milling disk has radial bars 16 of varying lengths with suitably inwards open interspaces and transverse bars 17 suitably with inwards decreasing height as being mentioned above.

FIG. 5 shows in larger scale a cross section of two milling disks illustrating the form of the radial bars 16. The width of the manufacture are enlarged. it is for instance possible to mix percent spruce pulp with 50 percent semichemical birch pulp and get lower raw material costs. Suitable starting materials for the method according to the present invention. are spruce sulfite pulp, spruce sulfate pulp, pine sulfate pulp, pine sulfite pulp, birch sulfate pulp mixed with spruce or pine sulfite or sulfate pulp, eucalyptus sulfate pulp etc.

EXAMPLE '1 A spruce sulfite pulp having a refinement degree ofRl8-83. l and a dry content of 90 percent was treated according to the invention.

The speed of rotation of the disk in the refiner was about 1500 r.p.m. The milling means were radial bars having a height of 8 mm. in the milling zone and a distance from each other of 10 mm. at the periphery. The height of the transverse bars was 8 mm. at the periphery and 4 mm. in the middle of the milling zone. During the experiment the space between the milling means on the two disk was varied so that it amounted to 0.5, 1.0, 2.0 and 3.0 mm. respectively. The obtained fluff was tested on bulk and absorption characteristics, content of fiber bundles (percent) and fiber length distribution (according to the Bauer-Mc Nett-method described in Svensk Papperstidning 68 (1965), p. 230). The obtained results are given in table 1 below in which table also the characteristics for the starting pulp and from this by conventional method using a hammer mill produced flufi are given.

The bulk and absorption characteristics were tested in an apparatus were 4 g. conditioned fluff was subjected to varying pressure. To allow adirect comparison the values given in table 1 are measured at the same pressure (0.l2 kgJcm?) on the fiber system.

The content of fiber bundles (percent) is a measure of fiber agglomerates which do not pass a screen having a mesh of 3 mm.

TABLE 1 Fibre lengths in mm., percent Fibre Bulk, Absorption 0.833 0.417 0.208 bundles, cm. /g. g. liquid] 0.833 0.417 0.208 0.104 0.104 percent flufl g. flufi Disk space, mm.:

0.5 14. 7 29. 3 24. 1 15. 5 16. 4 7 8. 9 13. 2 1.0 42.0 26. 7 14. 4 7. 4 9. 5 10 9. 4 14. 0 2.0 4s. 0 24. 8 13. 5 6.5 7. 2 12 10. s 14. 9 3.0 52.4 23.0 12.2 4.5 0.9 15 12.1 15.3 Starting material. 56. 4 22. 3 10. 9 3. 8 6. 7 Conventional method... 51. 6 23. 4 12. 8 4. 8 7. 4 28 9. 8 12.

the gap 18 between the tops of the bars in the outer parts of As can be seen from the table the process according to the the milling disks is in the following referred to as the disk present invention makes it possible to produce adisintegrated spa dry cellulose having a fiber distribution equivalent to the one Roll pulp is only produced by a few manufacturers which is Obtained y the convemmnal method but improved pa disadvantage and only from long-fibered pulp, i.e. spruce tron characteristics and weight by volume and a considerably pulp. The process according to the invention makes it possible l'edlwed Content of fiber bundles- Moreover, y using Sheet to use any type of pulp provided that it contains or h h pulp the costs of the produced disintegratedcellulose are remixing with another pulp is brought to contain enough longmarkably reducedfibered material, which is necessary for the absorption characteristics of the obtained fluff. Thus, the pulp being fed into the EXAMPLE shredder should contain at least 50 percent of long-fibered A pine sulfate pulp having a refinement degree of Rl8-83.7 material, i.e. material having an average fiber length of about d a d i h f 94 percent was tr t d according t the l mm. By mixing short-fibered and long-fibered matenalacmethod in example 1. The obtained results are given in table cording to the invention the possibilities to reduce the costs of 2.

TABLE 2 Fibre lengths in mm., percent Fibre Bulk, Absorption 0.833 0.4l7 0.208 bundles, em.?/g g. liquid/ 0.833 0.417 0.208 G.104 0.104 percent flufi I g. flufi EXAMPLE 3 A spruce sulfite pulp according to example 1 was mixed with a semichemical birch pulp (produced with a yield of 85 percent) in the ratio 50:50 and was treated according to the 5 method in example I. The results are given in table 3.

rotation of the rotating milling disk is within the range from about 500 to about 2000 r.p.m.

milling means'operating against a fixed strainer.

TABLE 3 Fibre lengths in mm., percent Fibre Bulk, Absorption 0.S33 0.417 0.208 bundles, cmJ/g. g. liquid! 0.833 0.417 0.208 0.104 0.104 percent flufi g. flufi Disk space, mm

0.5 12. 4 30. 1 22. 5 13. B 21. 2 14 8. 6 12. 1 1.0 31. 5 28. 4 18. 4 9. 7 12. 18 9. 2 13. 4 2. 38. 1 26. 7 16. 6 9. 0 9. 6 20 10. 1 14. 1 3.0. 39. 7 26. 2 15. 8 9. 3 9. 1 21 10. 3 l4. 2 Starting material 47. 1 25. 6 14. 8 7. 3 5. 2

We claim: 5. A process in accordance with claim 4 in which the l. A process for producing disintegrated dry cellulose fibers from cut pulp sheets which comprises shredding dry cut pulp sheets having a dry content above about 85 percent by weight into particles, entraining the shredded pulp particles in a stream of carrier gas, transporting the gas-entrained particles to the gap between two milling disks of which one is fixed and one is rotatable, the width of the gap being within the range from about 0.1 to about mm., subjecting the particles while in said gap to milling by the milling disks until the shredded pulp particles are disintegrated, and the fibers liberated, and then removing the disintegrated pulp fibers peripherally from the gap while entrained in the gas stream.

2. A process in accordance with claim 1, in which the width of the gap is within the range from about 0.5 to about 3 mm.

3. A process in accordance with claim 1, in which the rate of shredded pulp particles are strained through openings within the range from about 1 to about 5 cm. in width.

6. A process in accordance with claim 1 in which the dry content of the pulp is at least 93 percent by weight.

7. A process in accordance with claim 1 in which the milling disks are provided with milling means in the form of substantially radial bars or projections.

8. A process in accordance with claim 1 in which the pulp is shredded in a pin-type mill.

9. A process in accordance with claim 1, in which the milling disks are provided with milling means in the form of substantially transverse bars or projections.

10. A process in accordance with claim 1, in which the milling disks are provided with milling means in the form of substantially radial and transverse bars or projections.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 596 34p Dated August 3 l 1971 Inventm-(S) Nils Verner Biomqvist It is certified that error appears in the above-identified patent; and that said Letters Patent are hereby corrected as shown below:

On the cover sheet, Abstract line 6, "0.5 mm" should read 5 mm.

Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. A process in accordance with claim 1, in which the width of the gap is within the range from about 0.5 to about 3 mm.
 3. A process in accordance with claim 1, in which the rate of rotation of the rotating milling disk is within the range from about 500 to about 2000 r.p.m.
 4. A process in accordance with claim 1, in which the pulp is shredded in a hammer-type mill having hammer-shaped milling means operating against a fixed strainer.
 5. A process in accordance with claim 4 in which the shredded pulp particles are strained through openings within the range from about 1 to about 5 cm. in width.
 6. A process in accordance with claim 1 in which the dry content of the pulp is at least 93 percent by weight.
 7. A process in accordance with claim 1 in which the milling disks are provided with milling means in the form of substantially radial bars or projections.
 8. A process in accordance with claim 1 in which the pulp is shredded in a pin-type mill.
 9. A process in accordance with claim 1, in which the milling disks are provided with milling means in the form of substantially transverse bars or projections.
 10. A process in accordance with claim 1, in which the milling disks are provided with milling means in the form of substantially radial and transverse bars or projections. 